Ventilated ceiling constructions



1952 F. HANSON ET AL 3,058,411

VENTILATED CEILING CONSTRUCTIONS Filed Dec. 50. 1959 INVENTORS FasocmcnL. HAusou BY WILLIAM AJAcK Unite States atent fiice 3,058,411 PatentedOct. 16, 1962 This invention relates to ventilated acoustical ceilingconstructions; more particularly, it relates to an acousticalconstruction comprising false ceilings for room compartments and acommon plenum chamber thereabove, and which construction utilizes thecommon plenum chamber as a ventilating duct, with provision being madein the false ceilings for the absorption of sound and the passage ofventilating .air into or out of the common plenum chamber.

In many ventilating and acoustical constructions, wherein false ceilingsare used to enhance the esthetic eifect of room interiors and to providefor sound absorption, it has become quite common to utilize the plenumchamber formed between the false ceilings and a base construction, suchas, for example, the true ceiling or the basic framework of a building,as a return or a supply conduit for ventilating air. Since the basicframework of a particular building, including the main bearing portions,is ordinarily constructed long before the individual room compartmentsare formed, the walls of the individual room compartments need notextend fully to the basic framework ceiling, but only to the falseceiling or slightly thereabove. As a result, the plenum formed betweenthe false ceilings and the overhead basic structure is common to aplurality of room compartments. Where such a plenum chamber is used as areturn or supply duct or conduit for ventilating air and flow passagesare provided in the false ceiling for the ingress or egress ofventilating air, sound waves are capable of escaping from a roominterior through the flow passages in a suspended ceiling, thereby topass through the plenum chamber and the grillwork in an adjacent roomcompartment, and to enter such adjacent compartment. Thus, in a sense,where a common plenum chamber exists between a plurality of roomcompartments, such compartments are not necessarily acoustically sealedone from the other if the chamber is used as a fluid conduit.

In brief, the present invention comprises a perforated false ceilingsuspended from a base construction to form a plenum chambertherebetween, which chamber is common to a plurality of adjacent roomcompartments and is used as a fluid duct of a conditioning system. Soundabsorbing pads are superposed over a major portion of each falseceiling, .and sound traps are provided over selected areas of each falseceiling, not covered by a sound absorbing pad; the remaining areascomprise conventional structure, as, for example, lighting troughs,irnperforate pans, and the like. Each sound trap has provided therein aneffective passage therethrough for ventilating air, so that effectivepneumatic communication is obtained between each room interior and thecommon plenum chamber. In addition, each sound trap isso constructedthat the sound waves tending to escape through the fluid ducts withinthe trap are effectively absorbedythereby blocking off the passage ofsuch sound waves from one compartment to an adjacent compartment via thecommon plenum chamber and the air distributing means of the adjacentcompartment.

An object of the present invention therefore is to provide a novelventilating and acoustical ceiling having a plenum chamber thereover.

An additional object of this invention is to provide a ventilating andacoustical ceiling having thereover a plenum chamber utilized as an airconduit, with sound traps provided in the ceiling which allow the properflow of air therethrough and which also absorb the sound tending toescape or pass through the air passage means within the ceiling to anadjacent room compartment via the common plenum chamber.

Still an additional object of this invention is to provide a suspendedventilating and acoustical ceiling having a plenum chamber thereoverutilized as a fluid conduit and having simple but effective sound trapstherein which provide for the passage of ventilating air therethroughand at the same time effectively .absorb the sound waves received bysuch sound traps.

Still an additional object of this invention is to provide a ventilatingand acoustical ceiling having sound traps therein which allow thepassage of ventilating air therethrough and also provide for eifectivesound absorption, wherein the ceiling need not be specially adapted toaccommodate the traps, thereby permitting to be maintained a consistentdesign pattern or esthetic appearance produced by the members comprisingthe false ceiling.

These and other objects will be readily apparent from the precedingbrief description and the following more detailed description andappended drawings wherein:

FIG. 1 is a cross-sectional, perspective view of a plurality of roomcompartments showing primarily the ceiling of the present invention;

FIG. 2 is an enlarged perspective View, in cross-section, of anexemplary embodiment of the sound trap used in j the ventilating andacoustical ceiling illustrated in FIG.

1; and

FIG. 3 is a perspective view, partially broken away for purposes ofclarity,'of an additional exemplary embodiment of a sound trap capableof being used in the ceiling illustrated in FIG. 1.

Referring to FIG. 1, the basic framework 1 of a building, in itssimplest form, comprises a plurality of walls 1b supporting a ceiling1a. For the purposes of this invention, the ceiling 1a may be consideredto be the true ceiling of a room interior, even though the ceiling maybe open, as, for example, when it is comprised of only the basic girderor joist construction. The area enclosed by the basic framework 1 can bedivided into a plurality of individual room compartments by the erectionof a plurality of partitions 2, where necessary, and the provision offalse ceilings 3 for the wall enclosed areas. The ceilings may besuspended from the true ceiling 1a in any conventional manner, such as,for example, by the suspension system disclosed in United States Patent,Serial No. 2,401,906, issued to C. B. Burnett et al., on June 11, 1946.

Each ceiling 3 may comprise a plurality of sheet-like members 5juxtapositioned in a manner so as to form a planar type ceiling. Themembers may be in true sheet form, or the members may comprise aplurality of panlike members supported from the basic framework 1. inthe exemplary false ceiling construction disclosed herein, the members 5are of the pan-like type, as, for example, disclosed in United StatesPatent, Serial No. 2,334,484, issued to J. Y. Dunbar on November 16,1943. It is to be understood, however, that numerous other types ofindividual ceiling members may be used without departing from the scopeand intent of this invention.

The members 5 are perforated at least over the visible portions thereofand have superimposed thereover, except for selected areas swbjacent thesound traps, a layer 6 of sound absorbing material. The latter absorbsthe sound waves emanating from the room interior and passing through theperforations 5a in the ceiling members 5. The layer 6 comprises aplurality of individual sound absorbing pads 7 situated within each ofthe pans of the ceiling 3. The pads are of the type, for example, shownin United States Patent No. 2,401,906 or in United States Patent No.2,357,115 issued to W. A. lack, Bid, on August 29, 1944.

If desired, selected pans may be removed from within the false ceilingand replaced by lighting troughs 5b, usually of the type which areadapted to be received precisely within an area covered by one or morepans.

The plenum chamber 4 formed between the false ceilings and the trueceiling is common to the exemplary room compartments 2b, illustrated.Such chamber is therefore adaptable to be used as a fluid conduit, inthe event an air conditioning system is used as the heating and coolingsystem. to condition the room interiors. For example, the ventilatingheating or cooling air may enter the room compartments through a supplygrill 14 from a pressure source, such as a circulating fan, and exhaustinto the common plenum chamber 4 through selected areas of the falseceiling via the perforations 5a therein, which areas have removedtherefrom the superposed sound absorbing pads. From the chamber, the aircan be directed to a conduit 15 by an exhaust fan (not shown) andreturned back to the conditioning apparatus and the blower system forresupply to the room compartments 2b, 20.

However, with such a plenum chamber duct system, the air is not onlyeflfectively passed through the ceiling, but a portion of the soundWaves emanating from room 21), for example, is also undesirablypermitted to escape through the fluid exhaust areas within the ceiling.These waves also travel through the common chamber 4 and enter chamber20, for example, through a fluid exhaust system within its ceiling 3. Inorder to provide a proper fluid flow system within the ceiling and tosuppress or absorb such escaping sound waves, a sound trap 8 is utilizedover selected areas of the false ceiling 3, while the remainder of theceiling is superposed by the sound absorbing pads.

In an exemplary embodiment thereof, referring to FIGS. 1 and 2, thesound trap comprises a block of sound absorbing material of a sizesuitable to fit Within a pan 5. For example, since the pans areordinarily 12" x 24-, the block 8 is slightly less than 12" x 24 inorder to be received within the upturned edges of the pan. The trap 8was laminated from a plurality of relatively thin layers of soundabsorbing material; in the exemplary embodiment shown, four layers, 9,10, 11, and 12, were used, each of which was approximately 1" to 1% inthickness. A plurality of openings or ports 13 were formed completelythrough the laminated block, each of which was /2 in diameter, with 180holes being formed therein. In an ordinary room compartment, forexample, approximately 14 x 14, or thereabouts, one or two sound trapsacting as connecting ducts are all that are ordinarily necessary toaccommodate the flow of air therethrough. The particular size of theholes and the number of holes are not critical and are governed by theamount of air necessary to be passed through the sound trap. However,the size and number of the holes should be such that an appreciablefluid pressure drop is not created; at the same time, the holes shouldnot be so large as to freely permit the passage of soundwavestherethrough without appreciable absorption thereof.

Where the common chamber 4 is used as an exhaust duct, a pressuredifferential must be maintained between the chamber and the roominterior to provide for the proper air circulation. However, such adifferential not only continually passes air through the sound trap butalso leaks air through the openings between panels 5 subjacent the soundabsorbing pads 7. Although the rate of air leakage is relatively minute,over an extended period of time such leakage will cause contamination ofthe finished false ceiling adjacent the openings. To eliminate suchcontamination and also to provide for fiow primarily through the soundtrap and the pans subjacent the trap only, whereby the openings of thesound trap may be precisely designed for a particular flow of air, anair impervious septum 30 is superposed over the sound absorbing pads.Such septum prevents the flow of air through and around the pads andthrough the perfor-ations in the subjacent pans 5. The septum 30 may bea kraft paper, for example, applied as a continuous sheet over the soundabsorbing pads or as individual sheets over the individual pans.Numerous other types of septums may be utilized, if so desired, as, forexample, sheets of metal, aluminum foil, and sheets of plastic material.With sheets of metal or foil, an additional advantage is obtained inthat such sheets may be used as sound attenuation members, assisting toprevent sound waves from entering the plenum chamber or, if they arewithin the plenum chamber, from passing therefrom into subjacent roomcompartments. Where the common cham ber 4 is used as an air supply duct,the septum 30 can also be used, as it assists to confine the flowthrough the sound trap.

In an additional exemplary embodiment of the sound trap of the inventionand where, as in the previous embodiment described, pans 5 are utilizedto form the false ceiling, a layer 20 of sound absorbing material isseated within each pan receiving a sound trap (FIG. 3). The layer may beof the same over-all size and of the same type as the size and type ofsound absorbing pads 7 of FIG. 1. A plurality of relatively largeopenings 21 were made in the layer, which openings act as fluid conduitsfor the air passing into or out of the room interior. In the instantembodiment, three square cut-outs were formed, each of which was 3 on aside. A plurality of small blocks 22 were centrally located along theedges of the sound absorbing layer 20, and a second layer 25 of soundabsorbing material was rested upon the blocks to be spaced from thefirst layer 20 a distance equal to the thickness of the blocks 22. Thelayer 25 was comprised of a pair of laminated sound absorbing pads 26,24, each of which can be made from the same material and be of the sameoverall size as the sound absorbing pads 7 in the remaining pans of theceiling.

When the common plenum chamber 4 is used as an exhaust duct, the airexhausting from the room interior passes through the perforations 5a ofthe pans containing the sound trap, flows through the ducts 21, isdeflected transversely to the edges of the superposed layer 25 andenters the common plenum chamber 4. The sound waves received by thesound trap through the perforations 5a are for the most part initiallyabsorbed by the first layer 20. The sound waves entering duct 21 areabsorbed partially by the side walls of the duct and partially by thesuperposed layer 2'5. Since the layer 20 is approximately the samethickness as the thickness of the adjacent pads 7, the outlet passagesadjacent the edges of the sound trap are sufliciently above the adjacentpads 7 and the overlying septum 30, so that a relatively free flow ofair occurs over the pads and septum and no appreciable pressure drop orrestrictions to flow are created.

In each of the exemplary embodiments disclosed, the sound trap isapproximately four times the thickness of the adjacent pads. Since asimplified construction is used, the sound trap will usually be quitethicker than the adjacent pads, ranging usually between approximately 2to 4 times thicker than the adjacent pads. In the exemplary embodimentillustrated in FIG. 2, the thickness of the trap was four times thethickness of the adjacent pads 7, since four layers, each layer of whichis basically similar to an adjacent pad 7, are used. In the exemplaryembodiment illustrated in FIG. 3, each layer was basically the same asan adjacent pad. The thickness of the layers taken with the spacingmaintained for the proper air flow, resulted in a thickness of the trapalso approximately four times the thickness of any adjacent pad.

The theory of sound absorption between the two traps is the same eventhough the constructions differ slightly from each other. In the trap ofFIG. 2, sound absorption is obtained by the length of travel of thesound waves through the openings 13. During the passage of a wavethrough an opening, the wave is gradually absorbed along the lengththereof. In thetrap of FIG. 3, very little absorption is obtained duringpassage of a sound wave therethrough, since the openings 21 are quitelarge. Most of the sound absorption is obtained when a wave encountersthe direct obstacle in its path of travel, which is the superimposedsound absorbing layer 25.

Any escaping sound waves must, of course, pass through a pair of soundtraps before entering an adjacent room compartment. Thus, a sound waveemanating from compartment 2b, for example, must pass through a soundtrap in the ceiling of this compartment before it can enter the commonchamber 4. The at least partially absorbed wave, if it is to enter thecompartment 20, must also pass through a sound trap 8 in the falseceiling of that compartment. In the event an air impervious septum 30 isnot used, additional sound absorption of the wave is also obtainedduring the waves travel through the common chamber.

With either basic acoustical approach noted, one of the markedadvantages of the present invention is the fact that the sound trap maybe fabricated from materials similar to the sound absorbing pads or fromother materials of a similar nature also commonly used in soundabsorbing installations, the pads of which materials are usually readilyavailable in standard sizes. For example, in the embodiment illustratedby FIGS. 1 and 2, the sound absorbing pads 7 were fabricated frommineral wool having a density of approximately 34 pounds per cu. ft.;however, other pads having densities below pounds per cut. ft. arecommercially available in many standard sizes and may be used. Therelatively homogeneous sound trap 8 was fabricated from a glass fibertype of acoustical pad of a density of approximately 3 pounds per cu.ft. Pads of this type were used for the sound trap, as they could beworked somewhat easier than the mineral wool pads. The glass fiber typepads are similarly available in a range of densities below 10 pounds percu. ft. and in many different standard sizes.

An additional advantage of the present invention is the fact that theproper sound absorption and air flow is provided for with either type ofsound trap described without disturbing the continuity and estheticeffect of the false ceiling. Thus, the areas of the ceiling used asfluid conduits need not be modified in any way to accommodate the airflow into or out of the plenum chamber 4. This is particularly importantin relatively large installations, wherein the ceiling continuity isoften maintained according to a basic design of ceiling in one roomcompartment.

Moreover, it is quite common in oifice installations to alter the sizeand/or number of room compartments from time to time by changing theposition of the nonload bearing partition walls. With such changes, itis necessary only to relocate the sound traps, where required, withoutcorresponding relocation of the subjacent perforated member 5.

While the invention has been described in rather full detail, it will beunderstood that these details need not be strictly adhered to and thatvarious changes and modifications may suggest themselves to one skilledin the art, all falling within the scope of the invention as defined bythe subjoined claims. For example, the efliciency of the system may beincreased slightly by the use of an air impervious septum 30 havingsound reflective characteristics. Sound waves attempting to leak intothe plenum chamber from a room interior through the gaps betweenadjacent pans or sound waves passing through the pads not completelyabsorbed thereby find this additional sound barrier in their path. Inaddition, sound waves passing through the plenum chamber cannot leakinto a room through the openings between the pans, but are reflectedback by the sound reflective septum.

What we claim is:

1. A ceiling construction for a room conditioned by ventilating aircomprising a base ceiling, a plurality of perforated sheet-like memberssupported from said base structure to form a suspended false ceiling,sound trap means superposed over selected areas of said sheet-likemembers, sound absorbing pads having a predetermined thicknesssuperposed over the remaining areas of the sheetlike members to absorbthe sound passing through the perforations in the subjacent members,said pads being substantially air impervious thereby impeding the flowof air between the areas above and below the false ceiling through thesubjacent pans, each of said trap means comprising a body of soundabsorbing material having an over-all thickness of approximately 2-4times the thickness of the pads, and said trap means having continuousperforations through the body of sound absorbing material permitting thepassage of ventilating air through the body of material while absorbingthe sound passing therethrough.

2. The ceiling construction of claim 1 wherein the sound absorbing padsare superimposed by an air impervious septum to prevent the passage ofair through the perforations in the members subjacent the pads.

3. The ceiling construction of claim 1 wherein the perforated sheet-likemembers comprise a plurality of perforated metallic bands.

4. A ceiling construction for each of a plurality of adjacent roomcompartments conditioned by ventilating air comprising a base structure,a plurality of sheet-like members having perforations therein suspendedfrom said base structure to form a false ceiling in each compartment,said ceilings being spaced from the base structure thereby forming acommon plenum chamber over the room compartments, with said chamberbeing used as a fiu-id duct for the conditioning air, sound trap meanssuperposed over selected areas of the sheet-like members of eachcompartment false ceiling, sound absorbing pads superposed over theremaining areas of the sheet-like members said pads being air imperviousthereby impeding the flow of air between the plenum chamber and the roomcompartment through the subjacent pans, said sound trap means havingopenings therethrough acting as a connecting fluid duct between the roominteriors and the common plenum chamber, said sound trap means beingcomprised of sound absorbing material having a density below about 10pounds per cu. ft. and being at least several times greater in overallheight than the height of the sound absorbing pads, said sound trapmeans effectively preventing the transmission of sound between roomcompartments while allowing conditioning air to pass therethrough.

5. A ceiling construction for a room conditioned by ventilating aircomprising a base ceiling, a plurality of sheet-like members supportedfrom said base ceiling to form, a suspended false ceiling, sound trapmeans superposed over selected areas of said sheet-like members, soundabsorbing pads superposed over the remaining areas of the sheet-likemembers to absorb the sound passing through the perforations in thesubjacent members said pads being substantially air impervious, each ofsaid trap means comprising a homogeneous mass of sound absorbingmaterial formed from .a plurality of juxtapositioned layers of soundabsorbing material, and said homogeneous mass having a plurality ofrelatively large size openings formed continuously therethrough allowingthe ventilating air to pass therethrough and through the subjacentperforations in a sheet-like member, and said relatively large sizeopenings being lined by sound absorbing material so as to assist ineffectively absorbing the sound Waves encountered by said body ofmaterial while permitting the ventilating air to pass therethrough.

6. A ceiling construction for each of a plurality of adjacent roomcompartments conditioned by ventilating air comprising a base structure.a plurality of perforated sheet-like members suspended in eachcompartment from said base structure .to form a false ceiling in eachcompartment, said ceilings being spaced from the base structure therebyforming a common plenum chamber over the room compartments, said chamberbeing used as a fluid duct for the ventilating air, sound trap meanssuperposed over selected areas of the sheet-like members of eachcompartments false ceiling, sound absorbing pads superposed over theremaining areas of the sheet-like members, said sound trap meanscomprising a body of sound absorbing material having an over-allthickness of approximately two to four times the thickness of the padsand having continuous passages therethrough permitting the passage ofventilating air through the body of material while absorbing the soundpassing therethrough, and means superposed over the sound absorbing padsassisting to prevent the leakage of air through adjacentpads and alsoassisting to attenuate the sound attempting to pass from one compartmentto another via the common plenum chamber.

References Cited in the file of this patent UNITED STATES PATENTS1,705,778 Munroe Mar. 19, 1929 2,172,771 Norris Sept. 12, 1939 2,180,945Morey Nov. 21, 1939 2,587,884 Palmer Mar. 4, 1952 2,692,547 Ericson Oct.26, 1954 2,718,383 Frenger Sept. 20, 1955 2,973,703 Jack Mar. 7, 1961

